Strips for tying cable harnesses and other items are known, said strips being used in the form of portions of a long supply of strip. Both ends of a strip loop wrapped around the item to be tied and tightened are secured by means of a lock. Provided within the lock are two serrated blocking devices, which act together in a blocking manner with a serration of a respective end of the strip loop (U.S. Pat. No. 4,680,834, GB-A 2055218, EP-A-488 051, EP-B-297 337).
At the beginning of the tying operation by means of a tool, a portion of the strip is pushed forward through a lock, its teeth being kept away from the oppositely directed teeth of the blocking devices. The strip is passed around the item in the form of a loop, the length of which is greater than the circumference of the item to be tied. Its leading, free end is then led back into the lock and secured there by means of one of the blocking devices, while the other end of the strip, joined to the supply of strip, is pulled back for the purpose of tightening. As this happens, its teeth slide along the teeth of the other blocking device, which may cause them to damage one another. The smaller the circumference of the items to be tied in comparison with the length of the loop initially formed, the greater the distance over which the end of the strip has to be pulled back during tightening. If items of a very small circumference are to be tied, it may happen that several teeth of the strip run past the teeth of the locks during a number of successive tightening operations and, as a result, are repeatedly stressed and possibly damaged before they are finally themselves used for the blocking function in a later tying operation. The instances of damage may then have the effect of reducing the blocking force. The teeth of the lock may also be damaged in the process. The probability of damage is all the greater the sharper the edges of the teeth in the locks. This sharpness of the edges has previously being considered to be necessary in order for the teeth of the lock to engage reliably in the teeth of the strip. This is even the case if the tips of the teeth of the strip are rounded off (U.S. Pat. No. 4,680,834, GB-A 2065218). Therefore, they are kept apart from one another during this operation. This must take place with a certain safety margin.
Apart from the reliability of the blocking engagement, there is a further reason why the teeth tips of known blocking devices are formed with sharp edges. This is that it is endeavored to make the engagement of the teeth of the blocking device into the teeth of the strip take place as close as possible to the tooth base, that is to say at the connection of the tooth to the continuous strand cross section of the strip, because otherwise there is the risk of the tooth of the strip bending and the tooth of the lock sliding off it.